From: zhichang <zhichang.yuan02@gmail.com>
To: Arnd Bergmann <arnd@arndb.de>
Cc: linux-arm-kernel@lists.infradead.org,
Zhichang Yuan <yuanzhichang@hisilicon.com>,
linuxarm@huawei.com, linux-kernel@vger.kernel.org,
lorenzo.pieralisi@arm.com, minyard@acm.org,
benh@kernel.crashing.org, gabriele.paoloni@huawei.com,
john.garry@huawei.com, liviu.dudau@arm.com,
zourongrong@gmail.com
Subject: Re: [PATCH V2 4/4] ARM64 LPC: support earlycon for UART connected to LPC
Date: Wed, 14 Sep 2016 19:26:22 +0800 [thread overview]
Message-ID: <6e890161-0cd8-6027-f4e5-a222ceddd597@gmail.com> (raw)
In-Reply-To: <7585762.SZVHZyJdka@wuerfel>
On 2016年09月08日 19:04, Arnd Bergmann wrote:
> On Thursday, September 8, 2016 6:04:31 PM CEST zhichang wrote:
>> Hi, Arnd,
>>
>> On 2016年09月07日 22:52, Arnd Bergmann wrote:
>>> On Wednesday, September 7, 2016 9:33:53 PM CEST Zhichang Yuan wrote:
>>>> From: "zhichang.yuan" <yuanzhichang@hisilicon.com>
>>>>
>>>> This patch support the earlycon for UART connected to LPC on Hip06.
>>>> This patch is depended on the LPC driver.
>>>>
>>>> Signed-off-by: zhichang.yuan <yuanzhichang@hisilicon.com>
>>>>
>>>
>>> I'm skeptical about this too. Is this just needed because the 8250
>>> earlycon support comes before the lpc bus initialization?
>> I think you wonder why early_serial8250_setup can not be used direclty for this earlycon of LPC uart.
>>
>> 1. the earlycon kernel parameter format of LPC uart is different from 8250. something like that
>> "earlycon=hisilpcuart,mmio,0xa01b0000,0,0x2f8". You see, there is one more parameter after the baudrate.
>
> We should never need to specify the addresses manually like this,
> it's actually supposed to work if you just list "earlycon" here.
Do you mean flat-tree earlycon?
Ok, will support this in V3.
>
> The first membase is apparently only used during setup:
>
> + writel(LPC_IRQ_CLEAR, device->port.membase + LPC_REG_IRQ_ST);
> + /* ensure the LPC is available */
> + while (!(readl(device->port.membase + LPC_REG_OP_STATUS) &
> + LPC_STATUS_IDLE))
>
> Why doesn't the firmware do this before handing off control of
> the kernel to the console?
This is a checking on the LPC controller status.
I think we can keep this here.
>
>> Hip06 LPC uart need two base addresses for earlycon.
>> 2. the IO type is mmio to introduce a memory base address to access LPC register file. But the real uart
>> IO type is UPIO_PORT. This is spcial...
>
> This sounds like a deficiency in the of_setup_earlycon() function,
> which can only handle MMIO addresses, and won't actually
> be able to understand nodes without a "ranges" property like
> you have here.
>
Yes.
The current of_setup_earlycon only support MMIO and the first reg property must be memory.
We can not support our LPC uart without any new code.
But we can implement a private earlycon setup function and register it to the __earlycon_table, things will be ok.
I will do it in V3.
Best,
Zhichang
> I think we need to add a special case for port ranges here.
>
> Arnd
>
next prev parent reply other threads:[~2016-09-14 11:25 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-09-07 13:33 [PATCH V2 0/4] ARM64 LPC: legacy ISA I/O support Zhichang Yuan
2016-09-07 13:33 ` [PATCH V2 1/4] ARM64 LPC: Indirect ISA port IO introduced Zhichang Yuan
2016-09-07 15:06 ` Arnd Bergmann
2016-09-08 7:45 ` zhichang.yuan
2016-09-08 13:23 ` Arnd Bergmann
2016-09-13 6:08 ` zhichang
2016-09-07 15:21 ` kbuild test robot
2016-09-07 13:33 ` [PATCH V2 2/4] ARM64 LPC: LPC driver implementation on Hip06 Zhichang Yuan
2016-09-07 15:27 ` Arnd Bergmann
2016-09-08 8:06 ` zhichang.yuan
2016-09-08 10:00 ` Arnd Bergmann
2016-09-13 6:31 ` zhichang
2016-09-14 12:34 ` Arnd Bergmann
2016-09-07 17:51 ` kbuild test robot
2016-09-07 13:33 ` [PATCH V2 3/4] ARM64 LPC: support serial based on low-pin-count Zhichang Yuan
2016-09-07 14:50 ` Arnd Bergmann
2016-09-08 9:51 ` zhichang
2016-09-08 9:58 ` Arnd Bergmann
2016-09-14 11:48 ` zhichang.yuan
2016-09-14 12:07 ` Arnd Bergmann
2016-09-07 13:33 ` [PATCH V2 4/4] ARM64 LPC: support earlycon for UART connected to LPC Zhichang Yuan
2016-09-07 14:52 ` Arnd Bergmann
2016-09-08 10:04 ` zhichang
2016-09-08 11:04 ` Arnd Bergmann
2016-09-14 11:26 ` zhichang [this message]
2016-09-14 12:36 ` Arnd Bergmann
2016-09-08 9:26 ` kbuild test robot
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